The invention described herein relates generally to alignment tools that generate optical alignment beams. More particularly, improved leveling mechanisms for automatically leveling the outputted beam(s) are described.
A variety of survey and carpentry tools have previously employed lasers. The first laser alignment tools were manually leveled as in U.S. Pat. No. 3,897,637 and U.S. Pat. No. 3,279,070. Subsequently, self-leveling instruments were employed to improve accuracy and reliability.
In one type of leveling instrument, an entire laser is suspended by a pendulum and leveled by gravity. For example, in U.S. Pat. No. 3,771,876 a Hexe2x80x94Ne laser and chassis are hung by a flexible support to create a plumb beam which is subsequently directed in the horizontal plane using a pentaprism. FIG. 1 herein shows that system, with the laser 4 hung by a wire 2 over a pentaprism 10. The beam exits by a window 14, while the pentaprism 10 is rotated by a motor 16. The pendulous oscillation of the laser 4 is damped out by a magnet 12. Alternative approaches have used viscous fluids to damp the oscillations.
Another laser leveling system is described in U.S. Pat. No. 5,184,406 and is shown in FIG. 2. A laser diode assembly 22 is mounted on a float 26, which is supported by a liquid 28 in a vessel 24. The laser beam remains plumb in spite of the tilt of the vessel. In another approach shown in FIG. 3, U.S. Pat. No. 5,144,487 uses a ball bearing pendulum. Platform 23 is suspended by a ball bearing pivot 25 within a housing 29. An optical assembly within the platform 23 generates multiple collimated laser beams 21 for alignment purposes. The platform motion is damped by eddy currents induced by a magnet 27. The use of several ball bearings makes the instrument expensive, large, and of limited accuracy and ruggedness.
In another distinct approach, a laser is rigidly mounted to a housing of the unit and a compensation means (typically, lensing devices) is used to correct for the tilt of the housing. For example, in U.S. Pat. No. 3,684,381, a thin film of oil 36 is contained by an upper window 34 and a housing 35 (shown in FIG. 4). This thin film of oil 36 is used to create a correcting prism which directs the downwardly directed laser beam 32 toward the plumb direction. The oil prism is formed by the upper level of the oil 36 which is level and a lower window 38 which is tilted. A laser source is mounted in a laser housing 30. This system is accurate only when two cells with oil of index of refraction 1.5000 are used. This system has proven inadequate due to the absence of a fluid having the desired properties over the normal temperature range. In addition, the meniscus of the oil film 36 at the edges of the chamber contributes to wave front errors. In the system of FIG. 4, a pentaprism 40 (which is typically spinning) directs the plumb beam into a horizontal plane.
Several methods have been developed to tilt compensate a laser beam using wires. For example, in U.S. Pat. No. 4,221,483 a pendulous lens hangs below a laser diode. As the housing is tilted, the lens motion under gravity is proportional to the tilt angle, which steers the laser beam to the plumb position. A pentaprism again converts the plumb beam to the horizontal plane. In a system described in U.S. Pat. Nos. 4,852,265 and 4,912,851 and shown in FIG. 5, a laser beam 41 is reflected from a mirror 43 on a platform 46 which is suspended from a single wire 44. The reflected laser beam 42 is compensated by the tilt of the platform under the force of gravity. The length and diameter of the wire are chosen so that when the housing of the unit is tilted exactly one degree, the platform tilts exactly one half of one degree. Because of the two-to-one relationship between mirror tilt and beam correction, the laser beam is restored to its plumb direction after being tilted. These patents also show laser diodes mounted on cantilevers which respond to housing tilt to correct the output beam.
Each of the foregoing laser leveling techniques and apparatuses suffers from accuracy limitations, ruggedness concerns, and/or the expense of the components. In particular, devices requiring pendulums require expensive low-friction joints to allow free motion of the laser. These low friction pendulums are subject to oscillations (at the slightest touch) that require a long time to settle. As a result, such pendulum devices require expensive, difficult to perfect damping mechanisms to overcome the oscillation problems. What is needed is a method and apparatus for overcoming these and other difficulties in a relatively low-cost laser level device.
In accordance with the principles of the present invention, an apparatus and method for achieving automatic beam leveling are disclosed.
In one embodiment, an optical level comprises an optical assembly for generating a light beam and a platform that supports the optical assembly. The embodiment includes a slip-stick mechanism that pivotably supports the platform for rotation in at least one degree of freedom. The slip-stick mechanism provides sufficient stiction to hold the platform in place even when the platform is tilted somewhat relative to level. The slip-stick mechanism also permits the platform to pivot with relatively lower friction when the stiction is overcome. The embodiment includes an actuator arranged to cause motion of the platform by supplying sufficient force to the platform to overcome stiction from the slip-stick mechanism.
Yet another optical level embodiment comprises an optical assembly for generating an output light beam and a platform that supports the optical assembly. As with the foregoing embodiment, a slip-stick mechanism and an actuator are included. The embodiment includes a sensor for providing signals that may be used to determine whether the platform is level. The sensor includes a detector light source, a position sensitive light detector, and a two-axis bubble level. The two-axis bubble level is positioned with respect to the detector light source and the position sensitive light detector, such that detector light produced by the detector light source is projected through the two-axis bubble level onto the position sensitive light detector. Because the two-axis bubble level is aligned with the output beam, the detector can determine whether the two-axis bubble level is leveled and thereby whether the output beam is leveled.
Yet another embodiment comprises a leveling assembly that includes a pivotably mounted platform capable of rotation in at least one degree of freedom. The platform also including an actuator arranged to cause motion of the platform by supplying sufficient force to tilt the platform. The platform also includes a sensor for providing signals that may be used to determine whether the platform is level.
In a related embodiment, the sensor comprises a detector light source for producing detector light and a position sensitive light detector that is sensitive to the detector light. A two-axis bubble level is aligned with the platform, such that when the two-axis bubble level is leveled, the platform is also level. The light source is positioned so that it projects the detector light through the two-axis bubble level onto the position sensitive light detector so that the detector can determine whether the platform is leveled.
In yet another related embodiment, the leveling assembly further comprises a slip-stick mechanism providing sufficient stiction to hold the platform in place even when the platform is tilted somewhat relative to level, while permitting the platform to pivot with relatively lower friction when the stiction is overcome; and, wherein, the actuator can cause motion of the platform by supplying sufficient force to the platform to overcome stiction from the slip-stick mechanism.
In another embodiment, the apparatus comprises a beam projecting element tiltably mounted such that the optical assembly can tilt about two axes and hold its position. The optical assembly is capable of generating at least one visible light beam. The apparatus also includes a driving element, which when appropriately activated can tilt the optical assembly about either of the two axes and a sensor element for determining if the light beams generated by the optical assembly are level. The apparatus also includes control circuitry for controllably activating the driving element to tilt the optical assembly in a manner so that the light beams are substantially level.
In a further embodiment, the apparatus includes a slip-stick mechanism that enables an optical assembly to move in response to torque applied by the driving element and prevents substantial movement or oscillation of the optical assembly in the absence of actuator induced torque.
In yet another embodiment, the principles of the present invention teach an apparatus for projecting a visible light beam in level or plumb direction, in spite of a tilted condition of the apparatus, the apparatus comprising a housing; an optical platform tiltably mounted in the housing such that it can tilt in two axes about slip-stick joints; an optical assembly mounted on the optical platform, the optical assembly capable of generating at least three orthogonal output light beams; an actuator element which, when appropriately activated, tilts the optical platform about said two axes; a sensor element for determining if the optical assembly is level; and, a control circuitry for controllably activating the actuator element to tilt the optical platform so that the output beams are level.
Another embodiment comprises a method for generating output beams in a level or plumb direction, in spite of a tilted condition of an optical assembly. The method comprises mounting an optical assembly such that the optical assembly can tilt about two axes and hold its position after being controllably tilted, the optical assembly capable of generating at least one visible light beam. The method further comprises sensing if the light beams generated by the optical assembly are level. In the event that the light beams generated by the optical assembly are not level, the optical assembly is controllably tilted to a new angle. The method further comprises sensing if the light beams generated by the optical assembly are level when the optical assembly is at the new angle. If the new angle is such that the light beams are not level, the optical assembly is controllably tilted to another angle. The method further comprises continuously sensing and tilting until the light beams are level.